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Abstract:

An ink jet recording method includes an image formation step of forming
an image on a recording medium having an ink-receiving layer by ejecting
an ink from an ink jet recording head and a humidification step of
humidifying a gap between the recording head and the recording medium, in
which in the image formation step, an ink containing a specified dye
represented by general formula (I) and a water-soluble organic compound
having an inorganic-organic balance value of 1.4 or more to 2.7 or less
is used.

Claims:

1. An ink jet recording method comprising: an image formation step of
forming an image on a recording medium having an ink-receiving layer by
ejecting an ink from an ink jet recording head; and a humidification step
of humidifying a gap between the recording head and the recording medium,
wherein in the image formation step, an ink containing a dye represented
by general formula (I) and a water-soluble organic compound having an
inorganic-organic balance value of 1.4 or more to 2.7 or less is used:
##STR00003## wherein in general formula (I), A, B, C, and D each
independently represent a six-membered ring having aromaticity, and at
least one of A, B, C, and D represents a pyridine ring or a pyrazine
ring; M's each independently represent a hydrogen atom, an alkali metal,
ammonium, or organic ammonium; E represents an alkylene group; X
represents a sulfo-substituted anilino group, a carboxy-substituted
anilino group, or a phosphono-substituted anilino group, and the
substituted anilino group may further contain one to four substituents of
at least one type of substituent selected from the group consisting of a
sulfonic acid group, a carboxy group, a phosphono group, a sulfamoyl
group, a carbamoyl group, a hydroxy group, an alkoxy group, an amino
group, an alkylamino group, a dialkylamino group, an arylamino group, a
diarylamino group, an acetylamino group, an ureido group, an alkyl group,
a nitro group, a cyano group, a halogen atom, an alkylsulfonyl group, and
an alkylthio group; Y represents a hydroxy group or an amino group; and
a, b, and c satisfy 0.ltoreq.a≦2.0, 0.ltoreq.b≦3.0, and
0.1.ltoreq.c≦3.0, provided that a+b+c=1.0 to 4.0.

2. The ink jet recording method according to claim 1, wherein the content
(% by mass) of the dye represented by general formula (I) in the ink is
in the range of 0.7% by mass or more to 2.0% by mass or less with respect
to the total mass of the ink, and wherein the mass ratio of the content
(% by mass) of the water-soluble organic compound with respect to the
total mass of the ink to the content (% by mass) of the dye represented
by general formula (I) is in the range of 5.0 times or more to 14.3 times
or less.

3. The ink jet recording method according to claim 1, wherein the
water-soluble organic compound in the ink has an inorganic-organic
balance value of 1.7 or more to 2.5 or less.

4. The ink jet recording method according to claim 1, wherein the ink
contains 1,5-pentanediol serving as the water-soluble organic compound
having an inorganic-organic balance value of 1.4 or more to 2.7 or less.

5. The ink jet recording method according to claim 1, wherein the
humidification step is performed by supplying humidified air into the gap
between the recording head and the recording medium, and wherein the gap
between the recording head and the recording medium is filled with an
atmosphere having a temperature of 35.degree. C. or lower and an absolute
humidity of 0.013 kg/kgDA or higher.

6. The ink jet recording method according to claim 5, wherein the
absolute humidity is 0.015 kg/kgDA or higher.

7. An ink jet recording apparatus comprising: an ink storage portion
configured to store an ink; an image forming portion configured to form
an image on a recording medium having an ink-receiving layer by ejecting
an ink from an ink jet recording head; and a unit configured to humidify
a gap between the recording head and the recording medium, wherein the
ink stored in the ink storage portion contains a dye represented by
general formula (I) and a water-soluble organic compound having an
inorganic-organic balance value of 1.4 or more to 2.7 or less:
##STR00004## wherein in general formula (I), A, B, C, and D each
independently represent a six-membered ring having aromaticity, and at
least one of A, B, C, and D represents a pyridine ring or a pyrazine
ring; M's each independently represent a hydrogen atom, an alkali metal,
ammonium, or organic ammonium; E represents an alkylene group; X
represents a sulfo-substituted anilino group, a carboxy-substituted
anilino group, or a phosphono-substituted anilino group, and the
substituted anilino group may further contain one to four substituents of
at least one type of substituent selected from the group consisting of a
sulfonic acid group, a carboxy group, a phosphono group, a sulfamoyl
group, a carbamoyl group, a hydroxy group, an alkoxy group, an amino
group, an alkylamino group, a dialkylamino group, an arylamino group, a
diarylamino group, an acetylamino group, an ureido group, an alkyl group,
a nitro group, a cyano group, a halogen atom, an alkylsulfonyl group, and
an alkylthio group; Y represents a hydroxy group or an amino group; and
a, b, and c satisfy 0.ltoreq.a≦2.0, 0.ltoreq.b≦3.0, and
0.1.ltoreq.c≦3.0, provided that a+b+c=1.0 to 4.0.

[0004] The output form of an image has rapidly shifted from a silver
halide process to an ink jet process because of an increase in the
quality of an image formed by an ink jet recording method. Under such
circumstances, an image is required to have higher fastness properties,
such as ozone resistance. For example, International Publication No.
WO2004/087815 discloses that the use of a phthalocyanine dye having a
specific substituent achieves high ozone resistance. Furthermore,
International Publication No. WO2007/091631 discloses that excellent
ozone resistance is achieved by the use of an azaphthalocyanine dye, in
which outer aromatic rings of a phthalocyanine skeleton are
nitrogen-containing heteroaromatic rings.

[0005] To achieve higher quality of an image in an ink jet recording
method, there have been advances in the minimization of an ink droplet.
An increase in the ejection stability of ink has also been required. To
improve the reliability, for example, Japanese Patent Laid-Open No.
11-268256 discloses a recording method by which recording can be
performed even on a material with low affinity to ink and which
suppresses scattering of water from ink droplets and clogging of a
recording head by humidifying a gap between a recording head and a
recording medium.

SUMMARY OF THE INVENTION

[0006] The inventors have conducted intensive studies and have found that
the use of the azaphthalocyanine dye described in International
Publication No. WO2007/091631 improves the ozone resistance of an image
formed on a recording medium having an ink-receiving layer. However, in
the case where an image is formed with ink containing the dye by an ink
jet recording method including a humidification step, feathering is
liable to occur. Furthermore, the degree of feathering is inferior to
that of a phthalocyanine dye described in International Publication No.
WO2004/087815. Feathering indicates a blur of an image formed using an
ink and is disadvantageous when a high-definition image is formed.

[0007] Accordingly, aspects of the present invention provide an ink jet
recording method capable of forming an image that suppresses the
occurrence of feathering even if a gap between a recording head and a
recording medium is humidified to improve the ejection stability of ink.
Furthermore, aspects of the present invention provide an ink jet
recording apparatus that provides the foregoing beneficial effects.

[0008] According to one aspect of the present invention, an ink jet
recording method includes: [0009] an image formation step of forming an
image on a recording medium having an ink-receiving layer by ejecting an
ink from an ink jet recording head; and [0010] a humidification step of
humidifying a gap between the recording head and the recording medium,
[0011] wherein in the image formation step, an ink containing a dye
represented by general formula (I) and a water-soluble organic compound
having an inorganic-organic balance value of 1.4 or more to 2.7 or less
is used:

##STR00001##

[0011] wherein in general formula (I), A, B, C, and D each independently
represent a six-membered ring having aromaticity, and at least one of A,
B, C, and D represents a pyridine ring or a pyrazine ring; M's each
independently represent a hydrogen atom, an alkali metal, ammonium, or
organic ammonium; E represents an alkylene group; X represents a
sulfo-substituted anilino group, a carboxy-substituted anilino group, or
a phosphono-substituted anilino group, and the substituted anilino group
may further contain one to four substituents of at least one type of
substituent selected from the group consisting of a sulfonic acid group,
a carboxy group, a phosphono group, a sulfamoyl group, a carbamoyl group,
a hydroxy group, an alkoxy group, an amino group, an alkylamino group, a
dialkylamino group, an arylamino group, a diarylamino group, an
acetylamino group, an ureido group, an alkyl group, a nitro group, a
cyano group, a halogen atom, an alkylsulfonyl group, and an alkylthio
group; Y represents a hydroxy group or an amino group; and a, b, and c
satisfy 0≦a≦2.0, 0≦b≦3.0, and
0.1≦c≦3.0, provided that a+b+c=1.0 to 4.0.

[0012] Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference to the
attached drawing.

BRIEF DESCRIPTION OF THE DRAWING

[0013] FIGURE is a schematic diagram of the main portion of an ink jet
recording apparatus according to aspects of the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0014] Embodiments of the present invention will be described below in
detail. Hereinafter, a dye represented by general formula (I) is also
referred to as a dye of general formula (I).

[0015] The inventors have found that in the case of forming an image on a
recording medium including an ink-receiving layer using an ink that
contains the dye of general formula (I) and a specified water-soluble
organic compound, the humidification of a gap between a recording head
and a recording medium suppresses the occurrence of feathering. That is,
contrary to our expectations, the occurrence of feathering of an image is
suppressed by performing humidification, compared with the case where
humidification is not performed at the time of image formation. It has
also been found that in the case of using an ink containing a dye which
has a copper phthalocyanine skeleton but which is different from the dye
represented by general formula (I), if humidification is performed, the
occurrence of feathering is noticeable, compared with the case where
humidification is not performed.

[0016] The inventors have conducted studies on the cause of the difference
described above and have concluded that the cause is attributed to a
phenomenon described below. When the gap between the recording head and
the recording medium is humidified, the ink-receiving layer of the
recording medium absorbs water, so that the amount of water in the
ink-receiving layer is increased, compared with the case where
humidification is not performed. In the case where an image is formed on
the recording medium in such a state using an ink, the ink is less likely
to penetrate because of the increased amount of water in the
ink-receiving layer, compared with the case where humidification is not
performed. Here, a general dye diffuses via water in the ink-receiving
layer while the absorption of the ink is inhibited, extending the range
in which the dye is fixed. Thereby, feathering occurs.

[0017] The dye of general formula (I) has a unique property in that when
the dye is present in ink together with the specified water-soluble
organic compound, the aggregability and nondiffusivity of the dye are
increased. In the case of using the dye of general formula (I) serving as
a coloring material of ink, it is believed that the dye does not diffuse
via water in the ink-receiving layer but adsorbs preferentially on the
ink-receiving layer because of the property while the absorption of the
ink is inhibited by humidification. The fact that the dye adsorbs on the
ink-receiving layer while the absorption of the ink is inhibited
indicates that the dye adsorbs on a narrow range (not diffused) compared
with the range of the ink-receiving layer on which the dye adsorbs in a
state in which the absorption of the ink is not inhibited without
humidification. In this way, the occurrence of feathering is suppressed
to some extent.

[0018] Here, the inventors believe that the reason the dye of general
formula (I) provides high aggregability and nondiffusivity when the dye
is present in ink together with the specified water-soluble organic
compound is that the dye has an azaphthalocyanine structure. A difference
between a common phthalocyanine and azaphthalocyanine is that at least
one of outer aromatic rings of the phthalocyanine skeleton is a
nitrogen-containing heteroaromatic ring. The nitrogen atom of the
nitrogen-containing heteroaromatic ring has a lone pair of electrons and
thus interacts electrically with a hydrogen atom or the like. So, an
azaphthalocyanine molecule is more likely to interact with another
azaphthalocyanine molecule than water molecules when the specified
water-soluble organic compound is present together with azaphthalocyanine
in ink, thereby increasing the aggregability and nondiffusivity.

[0019] Furthermore, in the case of performing humidification, advantages
due to the aggregability and nondiffusivity of the dye of general formula
(I) are intensified by the presence of the specified water-soluble
organic compound together with the dye in ink. The water-soluble organic
compound will be described below in detail. Humidification and the use of
an ink containing a water-soluble organic compound that has low
solubility in (affinity for) the dye of general formula (I) significantly
suppresses the occurrence of feathering.

Ink Jet Recording Method

[0020] An aspect of the present invention is characterized by including an
image formation step of forming an image on a recording medium having an
ink-receiving layer using the specified ink described above and a
humidification step of humidifying a gap between a recording head and a
recording medium.

Image Formation Step

[0021] In aspects of the present invention, the image formation step of
ejecting an ink from an ink jet recording head to form an image on a
recording medium having an ink-receiving layer is performed. In the image
formation step, an ink containing the dye of general formula (I) and a
water-soluble organic compound having an inorganic-organic balance (I0B)
value of 1.4 or more to 2.7 or less is used. An exemplary method for
ejecting an ink includes applying thermal energy or mechanical energy to
the ink. In aspects of the present invention, a method for ejecting an
ink by the application of thermal energy can be employed.

Recording Medium

[0022] The recording medium used in aspects of the present invention may
have an ink-receiving layer and can have a glossy surface or a
semi-glossy surface. Specifically, the recording medium can have an
ink-receiving layer on at least one surface of a support, the
ink-receiving layer mainly containing a pigment composed of, for example,
silica, alumina, or its hydrate, and optionally containing an additive,
for example, a binder or a cationic polymer. In aspects of the present
invention, in particular, a recording medium can have an ink-receiving
layer containing at least one of alumina and hydrated alumina. In the
recording medium, ink is absorbed by pores of a porous structure formed
of pigment particles to form an image with high quality.

[0023] With respect to a support, a support which is capable of being
provided with the ink-receiving layer and which has stiffness such that
the support can be conveyed by a conveying mechanism of an ink jet
recording apparatus can be used. An example of the support is paper
containing pulp or a filler. A recording medium may be used in which a
resin layer composed of, for example, polyolefin, is arranged on at least
one surface of a support and in which an ink-receiving layer is arranged
on the resin layer. Furthermore, a recording medium may be used in which
ink-receiving layers are arranged on both surfaces of a support.

[0024] The recording medium used in the ink jet recording method according
to aspects of the present invention may be cut into predetermined size in
advance. Alternatively, the recording medium may be a wound sheet in the
form of a roll, the wound sheet being to be cut into predetermined size
after the formation of an image.

Ink

Coloring Material

[0025] A coloring material contained in the ink used in aspects of the
present invention is the dye represented by general formula (I):

##STR00002##

wherein in general formula (I), A, B, C, and D each independently
represent an six-membered ring having aromaticity, and at least one of A,
B, C, and D represents a pyridine ring or a pyrazine ring; M's each
independently represent a hydrogen atom, an alkali metal, ammonium, or
organic ammonium; E represents an alkylene group; X represents a
sulfo-substituted anilino group, a carboxy-substituted anilino group, or
a phosphono-substituted anilino group, and the substituted anilino group
may further contain one to four substituents of at least one type of
substituent selected from the group consisting of a sulfonic acid group,
a carboxy group, a phosphono group, a sulfamoyl group, a carbamoyl group,
a hydroxy group, an alkoxy group, an amino group, an alkylamino group, a
dialkylamino group, an arylamino group, a diarylamino group, an
acetylamino group, an ureido group, an alkyl group, a nitro group, a
cyano group, a halogen atom, an alkylsulfonyl group, and an alkylthio
group; Y represents a hydroxy group or an amino group; and a, b, and c
satisfy 0≦a≦2.0, 0≦b≦3.0, and
0.1≦c≦3.0, provided that a+b+c=1.0 to 4.0. In aspects of
the present invention, the content (% by mass) of the dye represented by
general formula (I) in the ink may be in the range of 0.1% by mass or
more to 10.0% by mass or less, such as 0.7% by mass or more to 2.0% by
mass or less with respect to the total mass of the ink. A content of less
than 0.1% by mass can lead to an image having insufficient ozone
resistance. A content of more than 10.0% by mass can lead to insufficient
ejection stability of the ink.

[0026] In general formula (I), A, B, C, and D each independently represent
a six-membered ring having aromaticity, and at least one of A, B, C, and
D represents a pyridine ring or a pyrazine ring. Examples of the
six-membered ring having aromaticity include a benzene ring, a pyridine
ring, and a pyrazine ring. Among these rings, a pyridine ring can be
used. In aspects of the present invention, a dye can be used in which one
to three of A, B, C, and D is pyridine rings or pyrazine rings and in
which the remainder is a benzene ring.

[0027] In general formula (I), E represents an alkylene group. The number
of carbon atoms in the alkylene group is may be in the range of 2 to 12,
such as 2 to 6. Specific examples of the alkylene group include an
ethylene group, a propylene group, a butylene group, a pentylene group, a
hexylene group, a cyclopropylenediyl group, a 1,2- or
1,3-cyclopentylenediyl group, and a 1,2-, 1,3-, or 1,4-cyclohexylene
group. Among these groups, an ethylene group, a propylene group, and a
butylene group can be used.

[0028] In general formula (I), X represents a sulfo-substituted anilino
group, a carboxy-substituted anilino group, or a phosphono-substituted
anilino group. The substituted anilino group may further contain zero to
four substituents and even zero to two of at least one type of
substituent selected from the group consisting of a sulfonic acid group,
a carboxy group, a phosphono group, a sulfamoyl group, a carbamoyl group,
a hydroxy group, an alkoxy group, an amino group, an alkylamino group, a
dialkylamino group, an arylamino group, a diarylamino group, an
acetylamino group, an ureido group, an alkyl group, a nitro group, a
cyano group, a halogen atom, an alkylsulfonyl group, and an alkylthio
group. Specific examples of X include a 2,5-disulfoanilino group, a
2-sulfoanilino group, a 3-sulfoanilino group, a 4-sulfoanilino group, a
2-carboxyanilino group, a 4-ethoxy-2-sulfoanilino group, a
2-methyl-5-sulfoanilino group, a 2-methoxy-4-nitro-5-sulfoanilino group,
a 2-chloro-5-sulfoanilino group, a 3-carboxy-4-hydroxyanilino group, a
3-carboxy-4-hydroxy-5-sulfoanilino group, a
2-hydroxy-5-nitro-3-sulfoanilino group, 4-acetylamino-2-sulfoanilino
group, a 4-anilino-3-sulfoanilino group, a 3,5-dicarboxyanilino group, a
2-carboxy-4-sulfamoylanilino group, a 2,5-dichloro-4-sulfoanilino group,
and a 3-phosphonoanilino group. In general formula (I), Y represents a
hydroxy group or an amino group.

[0029] In general formula (I), for example, a sulfonic acid group, a
carboxy group, and a phosphono group may be in the form of a salt.
Examples of a counter ion that can form a salt include ions of alkali
metals, ammonium ions, and organic ammonium ions. Examples of the alkali
metal include lithium, sodium, and potassium. Examples of the organic
ammonium include alkylamines having 1 to 3 carbon atoms, such as
methylamine and ethylamine; and onium salts of mono-, di-, or
tri-alkanolamine having 1 to 4 carbon atoms, such as monoethanolamine,
diethanolamine, triethanolamine, monoisopropanolamine,
diisopropanolamine, and triisopropanolamine. An alkali-earth metal, for
example, calcium or magnesium, may be used as the counter ion.

[0030] Specific examples of the dye of general formula (I) include
exemplified compounds I-1 to 1-24 shown in Table 1. Table 1 shows groups
of A, B, C, D, E, X, and Y in general formula (I). The dye according to
aspects of the present invention is not limited to the exemplified
compounds described below as long as it has a structure included in the
structure of general formula (I) and it is included in the definition of
general formula (I). Because at least one of A, B, C, and D in general
formula (I) is a pyridine ring or a pyrazine ring, regioisomers with
respect to the position of the nitrogen atom are present. So, in the case
of synthesizing a compound, a mixture of these regioisomers is obtained.
It is difficult to isolate these isomers. Furthermore, it is difficult to
identify these isomers by analysis. Thus, the dye of general formula (I)
is usually used as a mixture. However, even when the dye contains these
isomers, the advantageous effects of aspects of the present invention are
obtained without change. So, in this specification, these isomers are not
distinguished. With respect to A, B, C, and D in general formula (I)
according to aspects of the present invention, the number of pyridine
rings may be in the range of 1 to 3 and even 1 to 2. Specifically, among
the exemplified compounds, exemplified compounds I-1 to I-3, I-10 to
I-12, and I-21 to I-23.

Water-Soluble Organic Compound Having IOB Value of 1.4 or more to 2.7 or
less

[0031] The inventors have paid attention to the ratio of an inorganic
value and an organic value, i.e., an inorganic-organic balance (IOB,
inorganic value/organic value), based on the theory of an organic
conceptual diagram, the IOB value serving as an index of the properties
of an organic compound. The organic conceptual diagram is a diagram in
which properties of an organic compound are divided into the organic
value that indicates covalency and the inorganic value that indicates
ionicity and in which they are plotted on rectangular coordinates with
the organic axis (horizontal axis) and the inorganic axis (vertical
axis). The organic value is substantially equal to the product of the
number of carbon atoms of a compound and 20. The inorganic value is
defined as the sum of inorganic values intrinsic to groups.

[0032] In reference 1 (Yosio Koda. "Yuki Gainen Zu-Kiso to Oyo-" ("Organic
Conceptual Diagram, Foundation and Application"); Sankyo Shuppan, 1984),
the inorganic values of about 80 groups are determined to date; for
example, the inorganic value of a hydroxy group is defined as 100.
Reference 2 (Ryohei Oda. "Teijin Taimusu" ("Teijin Times"), 22(9), 10-4
(1952)) describes the following: The organic nature in the organic
conceptual diagram corresponds to the lipophilicity (i.e.,
hydrophobicity) of a surfactant. So, the ratio of the inorganic nature to
the organic nature calculated on the basis of the chemical structure of a
surfactant has the same meaning as the hydrophile-lipophile balance (HLB)
of the surfactant. Conversely, the IOB value can be regarded as an index
that indicates the hydrophobicity of an organic compound.

[0033] The inventors have conducted studies and have found that the use of
the water-soluble organic compound that is less likely to dissolve the
dye of general formula (I) increases the aggregability and nondiffusivity
of the dye of general formula (I) in the ink-receiving layer of the
recording medium, thereby suppressing the occurrence of feathering. As
described above, the degree of hydrophobicity of the water-soluble
organic compound can be determined by the IOB value. The inventors have
paid attention to the solubility of the dye of general formula (I) and
have conducted studies of ranges of the IOB values of the water-soluble
organic compound. Thus, the inventors have concluded that the ink needs
to contain the water-soluble organic compound having an IOB value of 1.4
or more to 2.7 or less. The use of a water-soluble organic compound
having an IOB value of less than 1.4 or more than 2.7 fails to suppress
the occurrence of feathering. The water-soluble organic compound can have
an IOB value of 1.7 or more to 2.5 or less. In aspects of the present
invention, advantages of aspects of the present invention are provided as
long as the ink contains the water-soluble organic compound having an IOB
value of 1.4 or more to 2.7 or less. Thus, the ink may further contain a
water-soluble organic compound having an IOB value of less than 1.4 or
more than 2.7.

[0034] Examples of the water-soluble organic compound which has an IOB
value of 1.4 or more to 2.7 or less contained in the ink used in aspects
of the present invention are described below, and each of the numbers in
parentheses represents the IOB value. Examples thereof include
triethylene glycol (2.7), 1,4-butanediol (2.5), 1,5-pentanediol (2.0),
3-methyl-1,5-pentanediol (1.8), 1,2-hexanediol (1.7), 1,6-hexanediol
(1.7), triethylene glycol monobutyl ether (1.4), and 2-pyrrolidone (1.8).
They may be contained in the ink separately or in combination. In aspects
of the present invention, the water-soluble organic compound is not
limited to the foregoing compounds. Any water-soluble organic compound
may be used without limitation as long as it has an IOB value within the
range described above. In aspects of the present invention, among these
water-soluble organic compounds, 1,5-pentanediol can be used.

[0035] In aspects of the present invention, letting the content of the dye
represented by general formula (I) in the ink be A (% by mass), and
letting the content of the water-soluble organic compound having an IOB
value of 1.4 or more to 2.7 or less be B (% by mass), the following
relationship can be satisfied. The content A (% by mass) of the dye
represented by general formula (I) in the ink is in the range of 0.7% by
mass or more to 2.0% by mass or less with respect to the total mass of
the ink. In addition, the mass ratio (B/A) of the content B (% by mass)
of the water-soluble organic compound having an IOB value of 1.4 or more
to 2.7 or less to the content A (% by mass) of the dye represented by
general formula (I) may be in the range of 4.5 times or more to 20.0
times or less and even 5.0 times or more to 14.3 times or less with
respect to the total mass of the ink. A mass ratio of less than 4.5 times
or more than 20.0 times can fail to strike a balance between the content
of the dye and the content of the water-soluble organic compound having
the specified IOB value, thereby failing to sufficiently suppressing the
occurrence of feathering. In particular, a mass ratio of more than 20.0
times can lead to an excessively high content of the water-soluble
organic compound having the specified IOB value, thereby increasing the
viscosity of the ink and failing to sufficiently providing ejection
stability.

[0036] In aspects of the present invention, our attention is focused on
the affinity between the dye and the water-soluble organic compound. So,
the term "the water-soluble organic compound" having an IOB value, which
is determined by calculation, does not include coloring materials, such
as dyes and pigments, and additives as described below.

Aqueous Medium

[0037] The ink may contain an aqueous medium, which is a mixed solvent of
water and a water-soluble organic solvent, in addition to the
water-soluble organic compound having an IOB value falling within the
specified range. Deionized water and ion-exchanged water can be used as
water. The content (% by mass) of water in the ink can be in the range of
50.0% by mass or more to 95.0% by mass or less with respect to the total
mass of the ink. Examples of the water-soluble organic solvent include
monohydric and polyhydric alcohols, glycols, glycol ethers, and
nitrogen-containing compounds, which can be used for ink for use in ink
jet printing. These compounds may be contained in the ink separately or
in combination. The content (% by mass) of the water-soluble organic
solvent in the ink can be in the range of 2.0% by mass or more to 50.0%
by mass or less with respect to the total mass of the ink. In this case,
the content of the water-soluble organic solvent includes the content of
the water-soluble organic compound having an IOB value within the
specific range.

Additional Additive

[0038] The ink used in aspects of the present invention may contain a
solid water-soluble organic compound at room temperature, for example,
urea, its derivative, or polyhydric alcohol, e.g., trimethylolpropane or
trimethylolethane. Furthermore, the ink may optionally contain various
additives in addition to the components described above. Examples of the
additives include surfactants, pH adjusting agents, rust-preventive
agents, preservatives, fungicides, antioxidants, anti-reducing agents,
evaporation accelerators, chelating agents, and water-soluble polymers.

Humidification Step

[0039] An aspect of the present invention includes the foregoing image
formation step and a humidification step of humidifying a gap between a
recording head and a recording medium. The humidification step may be
performed to the extent that the ink-receiving layer of the recording
medium sufficiently absorbs water. An example of a humidification method
is a method in which humidified air is fed into the gap between the
recording head and the recording medium. In aspects of the present
invention, the humidification step is performed by supplying humidified
air into the gap between the recording head and the recording medium. The
humidification step can be performed in such a manner that the gap
between the recording head and the recording medium is filled with an
atmosphere having a temperature of 35° C. or lower and an absolute
humidity of 0.013 kg/kgDA or higher. Furthermore, the humidification step
can be performed in an atmosphere having a temperature of 35° C.
or lower and an absolute humidity of 0.015 kg/kgDA or higher. Here, the
term "absolute humidity" used aspects of the present invention indicates
an absolute humidity on a weight basis, i.e., the weight (kg) of water
vapor contained in humidified air with respect to the weight (kg) of dry
air as expressed by the unit kg/kgDA. The lower limit of the temperature
can be 25° C. or higher. As a precondition, the relative humidity
can be less than 100%. With respect to the humidification conditions, the
atmosphere can have a temperature of 25° C. or higher to
35° C. or lower and an absolute humidity of 0.017 kg/kgDA or
higher. In this case, the effect of improving the intermittent ejection
stability by humidification is high, and the relative humidity is less
than 100% in this temperature range. Thus, no condensation occurs on the
recording head, providing excellent ejection stability.

[0040] Aspects of the present invention, in addition to the humidification
step described above, a prehumidification step of humidifying a recording
medium can be performed before the image formation step. In this step,
the recording medium is humidified before the recording medium is
conveyed to an image forming portion including the recording head. The
intermittent ejection stability is more effectively improved by
performing this prehumidification step. The reason for this is as
follows: The prehumidification step allows the recording medium to
sufficiently absorb water before the recording medium is conveyed to the
image forming portion. This makes it possible to effectively humidify the
gap between the recording head and the recording medium. In aspects of
the present invention, the prehumidification step is performed by
supplying humidified air before the recording medium is conveyed to the
image forming portion including the recording head. The prehumidification
step can be performed in an atmosphere having a temperature of 35°
C. or lower and an absolute humidity of 0.013 kg/kgDA or higher.

Ink Jet Recording Apparatus

[0041] An ink jet recording apparatus according to aspects of the present
invention includes an ink storage portion configured to store an ink, an
image forming portion configured to form an image on a recording medium
having an ink-receiving layer by ejecting an ink from an ink jet
recording head, and a unit configured to humidify a gap between the
recording head and the recording medium, in which the ink stored in the
ink storage portion is the ink described above.

[0042] The structure of the ink jet recording apparatus according to
aspects of the present invention will be described below. FIGURE is a
schematic diagram of an exemplary image forming portion 1 of the ink jet
recording apparatus used in the ink jet recording method according to
aspects of the present invention. The illustration of the entire
structure of the recording apparatus is omitted. A paper feeding unit,
the image forming portion 1, a cutting unit, a drying unit, the ink
storage portions, a control unit, and a paper ejecting section are
arranged from the upstream side to the downstream side of the conveying
direction of the recording medium. The paper feeding unit rotatably holds
a recording medium 2 wound in the form of a roll. The image forming
portion 1 includes a plurality of recording heads 1a corresponding to
inks of different colors. Here, four recording heads corresponding to the
four inks are arranged. However, the number of inks is not limited to
four. Each of the inks is fed from the ink storage portions to a
corresponding one of the recording heads 1a through ink tubes. Each of
the plural recording heads 1a is a line-type recording head provided with
an ink jet nozzle array that covers the maximum width of the recording
medium to be used.

[0043] In the image forming portion 1, a recording medium conveying path
is arranged transversely and faces the recording heads 1a. A conveying
mechanism configured to convey the recording medium is arranged along the
recording medium conveying path. The plural recording heads 1a and the
conveying mechanism are arranged in a substantially enclosed space in a
housing 1b. A second humidifying unit 1d configured to humidify the gap
between the recording heads 1a and the recording medium is arranged in
the image forming portion 1 and supplies humidified air into the gap
between the recording heads 1a and the recording medium (i.e., paper-head
distance). The humidified air may be fed not only into the gap between
the recording heads 1a and the recording medium but also into the whole
of the substantially enclosed space in the housing 1b to fill the whole
of the space with an atmosphere that satisfies predetermined temperature
and humidity conditions. Furthermore, a first humidifying unit 1c
configured to preliminarily humidify the recording medium before the
recording medium is conveyed to the image forming portion including the
recording heads may be arranged on the upstream side of the recording
heads 1a in the conveying direction.

[0044] The cutting unit is configured to cut the recording medium, on
which an image has been formed at the image forming portion 1, into a
predetermined size. The cutter unit includes a cutting mechanism. The
drying unit is configured to dry the cut recording medium in a short
time. The drying unit includes a hot-blast device provided with a heater
configured to heat a gas and a fan configured to generate the flow of the
heated gas, and a plurality of conveying rollers arranged along the
recording medium conveying path. The paper ejecting section is configured
to accommodate the cut recording medium ejected from the drying unit. A
plurality of pieces of the recording medium are stacked therein. The
control unit serves as a controller responsible for controlling and
driving the entire recording apparatus.

[0045] Note that the predetermined temperature and humidity conditions
described above can be achieved without performing the humidification
step, depending on an environment where the ink jet recording apparatus
is placed. However, the temperature and humidity in the outside
environment are always changed. So, the predetermined temperature and
humidity conditions are not always satisfied. Accordingly, the
achievement of the temperature and humidity conditions, which are set in
the aspects of the present invention, by performing the humidification
step remains effective in providing the advantages of aspects of the
present invention.

EXAMPLES

[0046] While the present invention will be described in more detail below
by way of Examples and Comparative Examples, the present invention is not
limited to the following Examples.

Preparation of Ink

[0047] Components (unit: % by mass) shown in Table 2 described below were
mixed and sufficiently stirred to dissolve the components. The resulting
solutions were filtered under pressure with a microfilter (manufactured
by Fujifilm Corporation) having a pore size of 0.2 μm to prepare inks.
Table 2 also shows the content A (% by mass) of the dye of general
formula (I) in the ink, the content B (% by mass) of the water-soluble
organic compound having an IOB value of 1.4 or more to 2.7 or less, and
B/A (times). Note that for the water-soluble organic compounds, each of
the numbers in parentheses represents the IOB value.

[0048] Acetylenol E100 is a nonionic surfactant manufactured by Kawaken
Fine Chemicals Co., Ltd. As exemplified compounds I-1 and I-10, compounds
synthesized on the basis of Examples described in International
Publication No. WO2007/091631 were used. Note that dyes of general
formula (I) are all mixtures. The mixtures of isomers and so forth are
referred to as "dyes". That is, the dyes include, for example,
regioisomers of compounds, regioisomers in terms of the position of the
nitrogen atom in a pyridine ring, isomers having different ratios of
benzo rings to nitrogen-containing heteroaromatic rings represented by A,
B, C and D in general formula (I), and α/β regioisomers of a
substituted or unsubstituted sulfamoyl group in a benzo ring. A
comparative compound was a dye having a structure in which ring A in
exemplified compound I-1 represents a benzene ring. As the comparative
compound, a compound synthesized on the basis of Examples described in
International Publication No. WO2004/087815 was used.

[0049] Ruled line patterns having a line width of about 0.44 mm were
formed on recording media (trade names: PT-101, SG-201, GL-101, and
GF-500, manufactured by CANON KABUSHIKI KAISHA) shown in Table 3 using
inks shown in Table 3 at a recording duty of 150%. During the formation
of each of the patterns, humidified air was fed in such a manner that an
atmosphere between a recording head and the recording medium had a
temperature and an absolute humidity shown in Table 3. For comparison,
the same ruled line patterns were formed at a temperature of 23°
C., a relative humidity of 50% (an absolute humidity of 0.009 kg/kgDA)
without humidification.

[0050] The recording media used were Canon Photo Paper Pro Platinum Gloss
PT-101, Canon Photo Paper Semi-gloss SG-201, Canon Photo Paper Gloss gold
GL-101, and PB PAPER GF-500 (all manufactured by CANON KABUSHIKI KAISHA).
In Table 3, these recording media are expressed as PT-101, SG-201,
GL-101, and GF-500. Here, PT-101, SG-201, and GL-101 are recording media
each including an ink-receiving layer. The ink-receiving layer of PT-101
contains hydrated alumina. The ink-receiving layers of SG-201 and GL-101
each contain silica. Note that GF-500 does not include an ink-receiving
layer and what is called plain paper.

[0051] An ink jet recording apparatus was used which included the image
forming portion illustrated in FIGURE. Specifically, the apparatus
included a recording head configured to eject ink by the application of
thermal energy, and a humidifying unit (second humidifying unit in
FIGURE) configured to supply humidified air into a gap between a
recording head and a recording medium at the time of image formation.
Recording conditions were set as follows: volume per ink droplet: 2.8 pL,
and resolution: 2400 dpi×1200 dpi. In aspects of the present
invention, an image formed under conditions in which eight ink droplets
each having a volume of 2.8 pL were applied to a 1/600 inch×1/600
inch unit region was defined as an image with a recording duty of 100%.
Then, the image was allowed to stand at a temperature of 23° C.
and a relative humidity of 50% for 24 hours to provide an evaluation
sample.

[0052] For the resulting evaluation samples, raggedness value Ra1
when humidification was performed and raggedness value Ra2 when
humidification was not performed were measured. The raggedness values
were measured with a personal image quality evaluation system (trade
name: Personal IAS, manufactured by Quality Engineering Associates). Then
the value of ΔRa was determined from ΔRa=Ra1-Ra2,
thereby evaluating the suppression of feathering by humidification.
Furthermore, the degree of feathering was evaluated on the basis of the
value of Ra1. In aspects of the present invention, the variation
degree of the line width of the ruled line was measured with the
evaluation system described above. When the raggedness value is small,
the line width of the ruled line is constant, which is excellent.
Evaluation criteria were described below. Table 3 shows the results. In
aspects of the present invention, according to the following evaluation
criteria, in the case where ΔRa was classified into grade C or
higher and where Ra1 was classified into grade C or higher, the
feathering was defined as an acceptable level. In the case where at least
one of ΔRa and Ra1 was classified into grade D, the feathering
was defined as an unacceptable level.

Evaluation Criteria of Suppression of Feathering by Humidification

[0053] A: ΔRa was -0.10 or less. [0054] B: ΔRa was more than
-0.10 and -0.05 or less. [0055] C: ΔRa was more than -0.05 and 0.00
or less. [0056] D: ΔRa was more than 0.00.

Evaluation Criteria of Degree of Feathering

[0056][0057] A: Ra1 was 1.60 or less. [0058] B: Ra1 was more
than 1.60 and 1.70 or less. [0059] C: Ra1 was more than 1.70 and
1.80 or less. [0060] D: Ra1 was more than 1.80.

[0061] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0062] This application claims the benefit of Japanese Patent Application
No. 2010-141940 filed Jun. 22, 2010, which is hereby incorporated by
reference herein in its entirety.